Our objective is to ascertain the importance of multiple forms of cytochrome P-450 as determinants of carcinogen metabolism. The cytochrome P-450 monooxygenases catalyze both the activation and detoxification of chemical carcinogens, and thus they often mediate the initial events in carcinogenesis. Multiple forms of the cytochrome have been isolated in our laboratory from rabbit liver microsomes. These forms can be distinguished by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, peptide mapping, immunological characterization, and enzymatic analysis. Using these techniques, we will determine the tissue distribution of the multiple forms. In addition, the ability of microsomes isolated from these tissues to activate carcinogens to mutagens in a Salmonella/microsome mutagenesis assay will be determined and correlated to the ability of the isolated cytochromes to mediate mutagenesis in the same assay system. We will also isolate additional forms of cytochrome P-450 and characterize them in this manner.